As a resistance change memory is mostly unaffected by miniaturization, its capacity can be increased, thus it attracts attention as a next-generation non-volatile memory.
The resistance change memory uses a reversible change in the resistance value of a resistance change element as a memory element for storing and discriminating data. The state of the resistance value of the resistance change element changes from the high-resistance state to the low-resistance state or from the low-resistance state to the high-resistance state by, for example, applying a voltage to resistance change films sandwiched between two electrodes and supplying a current to the resistance change film. An operation for shifting a resistance state of the resistance change element from the high-resistance state to the low-resistance state is called a set operation, and an operation for shifting a resistance state of the resistance change element from the low-resistance state to the high-resistance state is called a reset operation.
As the resistance change films of the resistance change element, a transition metal oxide film and the like are proposed. These resistance change films exhibit a high resistance value (insulating material) in an initial state immediately after they are formed. For this reason, during a production process of the resistance change memory in which the transition metal oxide film is used for the resistance change film, performed is a step called forming for shifting the resistance change film so as to have the low resistance value by supplying a current to the resistance change element while adjusting a voltage and forming a miniaturized current path called a filament in the resistance change film.
The resistance change memory in which the transition metal oxide film is used for the resistance change film has the following problems: it takes time to perform a step of forming; a large current flows in a circuit when performing a step of forming or a set operation, which destroys the resistance change film; when performing a reset operation for an element having too low a resistance value in a low-resistance state, a large current flows in a circuit which destroys a driving element or a protection element; a voltage value and a current value vary when performing a set operation and a reset operation; if the difference between a set voltage and a reset voltage is small, a determination voltage cannot be set at the reading operation time.
Moreover, when part of a filament formed by performing a step of forming is oxidized, or a metal oxide film is destroyed again, which may change the resistance value of the resistance change element, the increased number of rewriting data and the extension of the data hold time are in a trade-off relationship. For this reason, the reliability of the resistance change element as a memory element may not be ensured.